Studies of the mechanism of interaction of bovine neurophysins with oxytocin, vasopressin and small peptide analogs of the hormones will be continued. Specific projects include: 1) Determination of the entropic and enthalpic contributions of individual segments of the hormones to their free energy of interaction; 2) Measurement of the distance between the single neurophysin tyrosine and the binding site by NMR studies using nitroxide-spin-labeled analogs of the hormones; and 3) Chemical modification studies aimed at elucidating the role of the internally duplicated neurophysin sequences in the binding of hormone. Additionally, work in progress on the crystallization of neurophysin-peptide complexes will continue. BIBLIOGRAPHIC REFERENCES: Susan L. Lundt and Esther Breslow, "Electron Spin Resonance Studies of Neurophysin and its Interaction with Spin-labeled Peptides," J. Phys. Chem., 80, 1123 (1976). Abstract: Esther Breslow, "On the Importance of the Amino-Carboxylate Salt Bridge in Neurophysin-Hormone Complexes, Fed. Proc., 35, 1719 (1976).